The present invention relates to a power-on detector and a memory device including the power-on detector.
A semiconductor memory device is a data storage apparatus configured to store data and read out the stored data when it is desired. Memory devices may be classified into volatile memory devices and a non-volatile memory devices.
A volatile memory device loses stored data upon power-off. Random Access Memory (RAM) devices such as SRAM, DRAM, SDRAM, are typical volatile memory devices. A non-volatile memory device retains stored data even at power-off. Read Only Memory (ROM) devices such as ROM, PROM, EPROM, EEPROM, and flash memory devices, such as PRAM, MRAM, RRAM, FRAM, and the like are so-called non-volatile memory devices. Flash memory devices may be classified into NOR types and NAND types.
In general, a memory device is powered by an external power (voltage) source. At power-on, there power supply voltage provided from the external source may be gradually increased. The memory device may perform an initialization operation in response to a variation of the power supply voltage. After the power-on, elements of the memory device may perform read and write operations. Thus, at the power-on, a voltage level of the externally applied power supply voltage has to reach a voltage level sufficient to perform read and write operations without errors due to a voltage level of the externally applied power supply voltage.
The externally applied power supply voltage may be unstable at power-on. For example, the externally applied power supply voltage may include ripples. Though a stable voltage level of the externally applied power supply voltage is lower than a first voltage, a conventional power-on detector may judge the externally applied power supply voltage as stable as soon as it reaches a first predetermine voltage. Further, though a stable voltage level of the externally applied power supply voltage is lower than the first predetermined voltage, due to abnormal operation, a conventional power-on detector may prematurely judge the externally applied power supply voltage as stable as soon as it reaches a first voltage.